In the field of lighting equipment, the general trend for energy saving has been promoting widespread use of compact self-ballasted fluorescent lamps as an energy-saving light source alternative to ordinary electric lamps. Such compact self-ballasted fluorescent lamps are grouped into types with and without a globe. The type with a globe has, for instance, a called medium globe, which is similar to that of ordinary electric lamps, and has excellent appearance.
Such a compact self-ballasted fluorescent lamp has one or more glass tubes, and the glass tubes may be helical glass tubes or U-shaped glass tubes. Some compact self-ballasted fluorescent lamps have three or four U-shaped glass tubes. Here, a helical glass tube has been attracting attention, since it secures a larger arc length in a limited space inside a globe and therefore enables a high luminous efficiency to be realized.
As described above, glass tubes of various configurations are used for compact self-ballasted fluorescent lamps. Here, unevenness of luminance is sometimes observed in compact self-ballasted fluorescent lamps. To eliminate unevenness in luminance of a compact self-ballasted fluorescent lamp with a globe, conventionally, the thickness of a diffuser that is formed on the inner surface of the globe to diffuse light emitted from a glass tube is increased.
However, an increase in thickness of a diffuser poses the following problem. The increase inevitably causes the quantity of light emitted by a compact self-ballasted fluorescent lamp to attenuate, which lowers luminous efficiency. Accordingly, even though a helical glass tube is employed to realize high luminous efficiency, an attempt to eliminate unevenness of luminance causes luminous efficiency to be lower than expected.
In the light of the above problem, it is an object of the present invention to provide a compact self-ballasted fluorescent lamp that includes a glass tube that has been bent to form a helical configuration, in which unevenness of luminance is eliminated without causing a drop in high luminous efficiency, and a manufacturing method for the same.